Fire Triangle – A quick guide
The fire triangle is a basic principle in understanding how a fire ignites, and how it can continue to burn. The fire triangle, also known as the triangle of combustion, is made up of three components.
- A combustible substance or fuel (e.g. wood, paper, plastic etc)
- Oxygen, as a gas (usually from the air)
- A source of ignition (or heat)
If all these three factors are present and the conditions are right, the substance will catch fire (meaning heat and light will be produced accompanied by volumes of smoke and gases). Unless one or more of these components are removed from the fire, it will sustain and continue to burn.
Fuel consists of flammable and combustible materials that can be in any matter state. These can include:
- Combustible solids such as wood, paper, plastic, packaging materials, soft furnishings, fabrics and some metals e.g. magnesium
- Flammable solids in a powder form
- Flammable liquids such as petroleum and its derivatives, paints, solvents, oils etc
- Flammable gases such as hydrogen, LPG, methane etc
In order to remove the fuel section of the fire triangle, the fuel can either be doused by an extinguishing agent, or the fuel supply cut off, either deliberately by human hands or when the fuel supply runs out and the fire burns itself out naturally.
The vast majority of fires will require the presence of oxygen. There are unusual circumstances where chemical reactions that are combustion-like can be produced using materials such as chlorine, but otherwise oxygen will almost always be a part of a fire. The higher the concentration of oxygen in the air, the quicker the fire will burn.
Of course, oxygen is most commonly found in the air, however in certain workplaces there may also be additional sources such as oxygen cylinders, or oxidising agents.
The oxygen segment of the triangle is possibly the hardest to remove, since it is all around us. Oxygen can be removed from the fire by covering it, which is done through use of some types of fire extinguisher such as foam and carbon dioxide. If the fire can be contained and the oxygen level closed off, the fire can be eliminated.
The third section of the fire triangle can be easily overlooked. If a small amount of fuel and oxygen is heated by a certain degree, it will combust. As fires are exothermic, a small fire started by a tiny heat source is able to ignite more fuel and oxygen over and over until there is sufficient heat to establish and maintain a large fire. Heat can be provided by different sources of ignition.
Reducing the heat in a fire can be done in two ways. Firstly, by cooling through the application of water, dirt or another substance, and secondly by scattering the fuel to limit the possible effects of radiant heat.
Fire Triangle - Sources of ignition
There are many sources and this list is not exhaustive.
- Open flame e.g. matches, welding torches etc
- Electrical sparking sources – Spontaneous ignition
- Grinding sparks
- Static electricity
- Hot surfaces e.g. overheating equipment
- Sparks from electrical arcing, static discharge or metal tools
- Lasers and other radiant heat sources
- Some chemical reactions